It is well known amongst rifle and pistol enthusiasts that reloading by the enthusiast will result in cheaper ammunition. This requires the use of loading presses, amongst other equipment, to fit a projectile into a cartridge case.
Many such presses are known, and in the main they comprise a seat which holds the base of the cartridge in an upright position. This is necessary, since at this stage the cartridge normally contains the required charge of powder. A projectile is then placed onto the cartridge, or within a die such that the projectile is forced into the cartridge under movement of either a die or the seating arrangement which holds the cartridge.
Commonly, either a C-frame or O-frame press is used to hold the die assembly, and the cartridge is forced into the bore of the die wherein the bore of the die is closely shaped to the external surface of the cartridge, such that it is held firmly in position within the die. The projectile, which is located in a bore within the die above the cartridge, is held against the upper end of the cartridge by a seating stem which engages the upper portion of the projectile, and by movement of a ram from below the cartridge and by holding the seating stem stationary, and moving the cartridge upwardly, the projectile is forced into position in the cartridge.
In order to ensure the accuracy of ammunition, it is essential that the projectile be accurately positioned in the cartridge. Any angular misalignment of the projectile in relation to the cartridge will result in variations in the projectile trajectory once the ammunition is fired. In many circumstances of use of the ammunition, such as for sporting requirements, inaccuracies are tolerable. However, where the ammunition is being used for target shooting or any other accurate shooting, there is a requirement for the utmost accuracy in all equipment used. This includes the ammunition, and therefore great trouble is taken in relaton to correct alignment of the projectile in the cartridge.
Although there are many factors affecting the correct alignment of the projectile with respect to the cartridge such as sizing of the cartridge neck, tolerances of projectile diameter, and changes in the cartridge sizing due to repeated use, there are noticeable inaccuracies which result through misalignment of the loading die components.
In the common C-frame or O-frame press, where a ram moves a cartridge into a loading die, the loading die is secured within an upper arm of the press frame. As many different types of dies are commonly used in the one press, each loading die assembly is inserted into the upper arm by way of screw thread engagement. This, therefore, will result in both axial misalignment and angular misalignment of the loading die in relation to the ram of the loading die. Due to the sliding fits between the various components that comprise a loading die, such misalignment will result in eccentric forces being applied between the cartridge case and the projectile, which will then result in angular misalignment of the projectile in relation to the cartridge case.
In addition, although the forces involved in seating a projectile within a cartridge are relatively small, they are still sufficient to result in minute deflection of a C-frame press such that it slightly opens thereby resulting in further angular misalignment.